Today, there are many applications requiring broadband communications among various entities, which we broadly call “electronic components” herein. Examples of such electronic components are: the “daughter boards” of a mainframe computer or a super computer, the blade servers of a mainframe server, the computers and servers of a network computing system, the printers and other resources of network computing system, and so on.
Each of these systems is reaching bandwidth limitations arising from the use of electrical wiring for their interconnections. As an example, we look at mainframe and super-computers, which comprise hundreds to thousands of integrated circuit chips held and interconnected by “daughter boards,” each with tens to hundreds of IC chips per daughter board. In these systems, there is a need to convey electrical signals between IC chips located on different daughter boards. This is commonly accomplished by providing an electrical backplane, which comprises hundreds, and sometimes thousands, of electrical traces formed within a board, and a plurality of slot holders for the daughter boards. Each slot holder has electrical contacts that make electrical connections to corresponding electrical contacts disposed at the holding edge of its daughter board. The electrical contacts are in turn coupled to the electrical traces in the backplane, and in combination therewith, provide electrical interconnections between the daughter boards. Also, some of the electrical contacts provide power supply voltages to the daughter boards. Each slot holder typically allows its daughter board to be selectively removed for testing, repair, and/or replacement.
With the clock frequencies of computer systems now well into the Gigahertz range, there is an increasing need for signals between chips to move at the speed of light. However, the propagation speed of electrical signals through the electrical traces of the backplane is relatively slow compared to the speed of light.
There have been many approaches of using optical means to convey signals between daughter boards. One approach has been to use daughter boards with channel waveguides, and back planes with channel waveguides, with optical connectors between the channel waveguides of the boards and back planes. However, this system suffers from degradation in the optical quality of the optical signals as they travel from one daughter board to the back plane, and then to another daughter board. Another approach has been to transmit optical signals between adjacent daughter boards through the free space between them. However, the daughter boards must be precisely aligned with one another, which is time-consuming and requires expensive precision components. Despite these efforts, the optical signals in this system also degrade significantly in traveling between daughter boards. Still other approaches have addressed these problems by using extremely compact stacks of alternating layers of IC chips and optical waveguides, each layer being very thin. However, in these approaches, the steps of testing and replacing the layers of IC chips are difficult.
As another example of a system reaching its bandwidth limit, we look at the common network computing system, where file servers, printer resources, and banks of computers are electrically connected to a central host. Here, communications from one electronic component (e.g., a computer) and another (e.g., a file server or a printer) are routed through the central host. As the number of entities on the network grows, a communication bottleneck in the central host is reached in these systems. In addition, the electrical cables used to interconnect these devices limit the bandwidth as the cable distance increases, thereby placing limits on the geographical size of such networks and reducing communication bandwidth.